The role of nuptial gift proteins in sexual conflict in the decorated cricket

Sexual reproduction is a cooperative endeavor, but the interests of the two sexes frequently diverge. This leads to sexual conflict, which is common among insects. Males often manipulate female behavior and physiology to increase their share of paternity. One hypothesis posits that males of some species use a nuptial food gift, comprised of materials other than sperm, to achieve this. In the decorated cricket, Gryllodes sigillatus, these gifts take the form of a spermatophylax, a gelatinous mass forming part of the male spermatophore and consumed by the female after mating but prior to her removing the sperm-containing portion of the spermatophore. As spermatophylax feeding deters females from prematurely terminating sperm transfer, it enhances the paternity share of the male. Additionally, males might manipulate females even further through this route, to their own fitness benefit. Here, we focused on the effect of SPX1, which is the most abundant protein in the spermatophylax of male decorated crickets. We used RNA interference to generate a knockdown of SPX1 expression, and tested its effect on spermatophylax feeding duration and the latency to remate in females. We found that females fed for a shorter time on spermatophylaxes generated by SPX1 knockdown males, and that such females fed longer on the spermatophylax during a second mating with a control male. As such, SPX1 seems to play an important role in mediating sexual conflict in this species, enhancing paternity by increasing a male’s sperm transfer time, while decreasing that of a competitor in the next mating.